In the prior art of fluid injectors, also called fluid injection valves, it is known for a first valve and a second valve to act on the same fluid path. For example, reference is made to German patent application DE 10 201 3 222 030 A1. In such fluid injectors, which may be used for direct injection of a fuel gas into the combustion chamber of a combustion engine, its two valves must be operated contemporaneously. CNG-DI fluid injectors, i.e., fluid injectors which are used for direct injection of compressed natural gas, should have a “zero” tip leak, which cannot be achieved with standard metal-to-metal sealing. In order to achieve a good sealing against gas, an elastomeric material is preferred. However, elastomeric materials do not withstand the injector tip temperatures which are typical at the inside of a combustion chamber. For this reason, an elastomeric material is placed away from the combustion chamber in a “cold valve.” The other valve (the “hot valve”) is placed at the fluid injector inside the combustion chamber. The hot valve, which may have an injector design of the outward opening type, is required to keep the injector tip closed against the combustion pressure. The cold valve is required to achieve the intended “zero” tip leak in cooperation with the hot valve.
In those fluid injectors comprising a first valve and a second valve in the same fluid path, there is a need to control both valves. To operate the valves, it is known that the fluid injector comprises a solenoid, i.e., a pole piece which is surrounded by a coil, and an armature which is coupled to a valve and which may be attracted and moved towards the pole piece if the coil is energized by electric current. German patent application DE 10 201 3 222 030 A1 discloses a fluid injector wherein one solenoid is used to control the first valve and the second valve simultaneously. However, because the hot valve is of the outward opening type, this requires that also the cold valve is of the outward opening type which may be disadvantageous in case of a system failure mode when, for example, gas is delivered to the injector with a not controlled too high pressure.
As to other fluid injectors comprising a cold valve of the inward opening type, it has been proposed to apply two solenoids which can independently operate the inward valve and the outward valve. However, such fluid injectors are unsatisfying because of its complex and costly structure and because for controlling each of the both solenoids it is needed a dedicated power stage in the injector driver unit inside the engine control unit (ECU). In case two solenoids are required, this also means that two power stages for the individual injectors are required. If, in another design, two coils are used for pulling two armatures in the same direction (i.e., for a serial design) to increase the solenoid maximum force, a complex and expensive structure results which implies additional design difficulties for the controlling functions of both, hardware and software, of a CNG-DI injection system.